At harvesting, tobacco leaves contain a considerable quantity of water. After harvesting, this water is removed by various drying processes, as a result of which the leaf structure shrinks. During the usual processes for preparing tobacco for the manufacture of cigarettes and cigars, the tabacco regains, if any, only a small part of the original volume, so that a considerable loss in the filling capacity of the tobacco results. Due to this shrinkage the tobacco has a higher volume density than that required for the manufacture of cigarettes of satisfactory quality.
Numerous processes are known to improve the filling capacity of tobacco. This process is also known as tobacco expansion. It is common to these processes that the tobacco which is to be expanded is impregnated under defined pressure and temperature conditions with a volatile auxiliary. This auxiliary or flowing agent is then vaporized by supplying heat, reducing the pressure or both. The increase in the volume of the auxiliary, which then takes place, effects the expansion of the tobacco. The known processes for expanding tobacco differ primarily in the nature of the auxiliaries (blowing agents) which are employed. For example, the process according to German Patent Specification No. 1,917,552 uses volatile organic liquids, the process according to German Patent Specification No. 2,143,388 uses a mixture of ammonia and carbon dioxide, the process according to German Offenlegungsschrift No. 2,503,636 uses carbon dioxide and the process according to German Offenlegungsschrift No. 2,903,300 uses nitrogen or argon.
A substantial disadvantage of the processes mentioned above is that, although they lead to a useful expansion of the tobacco, the taste of the smoke from the tobaccos thus expanded is considerably impaired by the process. Not only is the taste intensity diminished, but the tobaccos treated in this way also have unfavorable taste features which, according to the statements of experts, can be described by the occurrence of less desirable taste notes, described as bitter, metallic, musty or rancid. Since the expanded tobaccos did not have these undesirable taste characteristics before their treatment, obviously they are caused by the treatment.
It is a generally known practice to treat tobacco leaves, before cutting, to improve or enrich the taste, with substances, such as sugar, liquorice, cacao, fruity syrups and the like. It is also known to add aroma substances to the finally cut tobacco for this purpose. For this purpose, natural and synthetically produced essences of any type, identical to the natural ones, or individual aroma substances, such as menthol or vanillin, are employed. The list of the substances and essences which can be used for this purpose is extensive. See e.g., the listing by Leffingwell et al., Tobacco Flavouring for Smoking Products, 1972. However, tests have shown that, in the case of expanded tobacco, the above described undesired taste properties caused by the expansion can be avoided, eliminated or covered only to a very unsatisfactory extent, if at all, by the conventional additions of aroma substances or flavorings either to the tobacco leaf or to cut tobacco.